The invention relates to a pump with a pump chamber with a rotary-driven pump element, at least one suction connection opening into the pump chamber and at least one pressure connection and with circulating pumping cells with changeable volumes that are each connected with the suction connection or pressure connection, depending on the rotary position of the pump element.
Pumps of the type addressed here are known e.g. as vane-cell and roller-cell pumps in which the pumping cells are delimited by the pump chamber wall and the pump elements, whereby the pump elements are designed either as vanes or rollers that are held by the rotary-driven pump element, which in this way forms the rotor of the pump. In these pumps, it is known that in operation they are subject to pressure pulsation, which on one hand develops because of the laws of pumping and on the other hand because of pressure compensation processes in the transition of the pumping cells from suction connection to pressure connection and/or from pressure connection to suction connection. In the prior art, an attempt has been made to control the pressure compensation processes by using small slots that are formed in the pump chamber walls and are in connection with the suction and/or pressure connection. A pump design of this type with slots is known e.g. from DE 196 26 211 A1.
However, it has been found that the pressure compensation processes cannot be controlled and/or influenced in a satisfactory manner in all application cases of the pump. In particular, with a high percentage of undissolved air in the pumping medium, pressure pulsations often play a dominating role because of the pressure compensation processes. In particular, this is the pressure compensation process that takes place when a pumping cell transitions from suction connection to pressure connection. Because of the amount of undissolved air in the pumping medium, the elasticity of the pumping medium is increased. In this case, greater volume flows are necessary to pre-stress the pumping medium in the pumping cell and thus to bring it to the proper pressure. This leads to problems especially during the pre-compression or pre-filling process, as it is called.
Problems also occur, especially if the degree of foaming in the pumping medium, i.e. the percentage of undissolved air in the pumping medium, is very different over the operating range of the pump. In the known pump with slots, no satisfactory compromise can be found in the slot design. Therefore, especially at the edges of the pump operating status spectrum, limitations in the control of the pressure compensation processes have to be taken into consideration, the edges of the operating status spectrum lying at low pumping pressure and a low degree of foaming and high pressure and a high degree of foaming. With low degrees of foaming in the pumping medium, smaller volume flows are required for the pressure compensation process than with greater foaming in order to obtain similar pressure gradients. The volume flow that takes place during flow through a slot is mainly dependent on the pressure difference that occurs and the cross section of the slot. The dependence of the volume flow generated on the elasticity of the pumping medium is almost insignificant so that the foaming and/or the degree of foaming of the pumping medium is not considered during the pressure compensation processes.
Therefore, it is the task of the invention to provide a pump of the type named at the beginning that does not have these disadvantages.
This task is solved with a pump that has a pump chamber in which a rotary-driven pump element is mounted. The pump also has at least one suction connection that opens into the pump chamber and at least one pressure connection. In addition, the pump has circulating pumping cells with changeable volume that are connected with the suction or pressure connection depending on the rotary position of the pump element. The pump according to the invention distinguishes itself in particular by a hydraulic intermediate capacity that can be stressed with the pumping medium pressure present at the pressure connection by way of its first connection and that, by way of its second connection, can be stressed with the pumping medium pressure present at the pressure connection depending on the rotary position of the pump element or it can be connected with a pumping cell that has no direct connection to the pressure connection. If both connections of the intermediate capacity are connected with the pumping medium pressure, this intermediate capacity will be charged. However, if the second connection of the intermediate capacity is connected to the pumping cell that is not connected to the pressure connection, the intermediate capacity discharges into this pumping cell. In this design according to the invention, it is advantageous for the intermediate capacity to have a certain elasticity, which on the one hand depends on its volume and on the other hand on the degree of foaming of the pumping medium itself. This means that at low degrees of foaming the storage effect of the intermediate capacity is low and it is high with high degrees of foaming. This is advantageous to the extent that, with low degrees of foaming, a correspondingly lower volume flow is also necessary in order to pre-stress the pumping medium in the cell. The pressure compensation process is determined mainly by the magnitude of the resistance connected in series in the two connections. With high degrees of foaming, a correspondingly higher volume flow is necessary, which is met by the large storage effect of the intermediate capacity at high degrees of foaming. With high degrees of foaming, the intermediate capacity is thus relieved at the beginning of the pressure compensation process in the direction of the pumping cell to be filled and in this period provides for a faster pressure increase. If this compensating process is completed, the operating pressure must now recharge both the cell to be filled and the intermediate capacity. This results in a pressure increase in the pumping cell that is more gradual overall. This more gradual pressure increase is advantageous and desirable because with a high percentage of undissolved air in the oil, the elasticity is high at lower pressure and lower at high pressure. This means the elasticity curve is very progressive. With low pressure in the pumping cell to be filled, this requires a higher volume flow, which is provided in that the intermediate capacity is relieved and/or discharged and at higher pressures in the cells to be filled, a lower volume flow is provided in that the intermediate capacity and the cell are charged.
According to an advantageous embodiment, the first connection of the intermediate capacity is connected to the pressure connection. This means that the first connection is directly in connection with the pressure connection on the pump chamber side. In this process, it is advantageous if the intermediate capacity is arranged in the immediate area of the pressure connection so that very long connectors between the pressure connection and the intermediate capacity are not necessary.
In a further development of the invention, it is provided that the second connection of the intermediate capacity opens into the wall of the pump chamber and is brushed over by the pump elements delimiting the pumping cells. In this way, it is especially easily possible to control the charging and discharging process of the intermediate capacity. This means that a charging and discharging of the intermediate capacity is insured based on the rotation of the pump element alone. This means that in an especially advantageous manner, additional control elements can be dispensed with. Because of the fact that the second connection opens into the pump chamber wall and in a preferred embodiment the first connection of the intermediate capacity is directly connected to the pressure connection, control of the charging and/or discharging process is carried out simply because of the fact that the pump elements brush over the openings of the connections so that the opening of the second connection is closed or released by the pump element and namely in such a way that both connections are connected with the pumping medium pressure or the first connection is stressed with the pumping medium pressure and the second connection is connected with the pumping cell to be filled. Overall, the result of this is an especially simple design in which the control can also be carried out very easily but still very reliably.
In a preferred embodiment, the intermediate capacity has about double the volume of one pumping cell. Because of variation of the volume, the elasticity of the intermediate capacity mentioned above can be adjusted so that the storage effect of the intermediate capacity can be coordinated to the degrees of foaming that are present.
Especially preferred is an embodiment in which a hydraulic resistance lies in the first and/or second connection of the intermediate capacity. This results in advantages during low degrees of foaming of the pumping medium, in which the pressure compensation process is mainly determined by the size of the resistances connected, preferably in series, to the intermediate capacity. The intermediate capacity itself has somewhat less of an effect with these degrees of foaming.
In one embodiment, it can be provided that the intermediate capacity is formed of at least two partial capacities which are connected in series in an especially preferred embodiment. Between the two partial capacities, a hydraulic resistance can be mounted. In a preferred embodiment, a series connection of partial capacity, hydraulic resistance and partial capacity thus results. If in addition hydraulic resistances are present in the first and/or second connections, they are also preferably connected in series so that overall only series connections of the hydraulic resistances and partial capacities result.
In a preferred embodiment, the intermediate capacities are formed in the pump housing. Alternatively or additionally, the intermediate capacity can also be arranged in the wall of the pump chamber, turned away from the pump chamber. Naturally, combination possibilities are also conceivable. If the intermediate capacity lies in the pump housing, it is still mounted very close to the pump chamber so that long connection paths for the intermediate capacity are avoided.
A preferred embodiment of the pump is characterized in that the pump chamber is formed of a pump chamber ring and at least one pressure plate lying on the face sides of the pump chamber ring and/or is delimited by the pump housing, whereby in a preferred embodiment a hydraulic resistance lies in one of the pressure plates and the intermediate capacity lies in the pump housing. In this way, the hydraulic resistances can be implemented by using simple openings with small cross section which simultaneously form the first and second connection of the intermediate capacity. Then the intermediate capacity lies behind the pressure plate as a recess that is covered by the pressure plate and is connected with the openings in the pressure plate. The intermediate capacity and/or at least one hydraulic resistance can thus lie in one of the pressure plates and/or in the pump chamber ring and/or in the pump housing.
In a preferred embodiment, the hydraulic resistance lies between the wall adjacent to the pump element and the wall turned away from this wall (outer wall) of the pump chamber. In this way, the hydraulic resistance can easily be produced by an opening, preferably a stepped opening.
In order to avoid leakage, in the design just mentioned, it is preferably provided that the transition from the hydraulic resistance to the intermediate capacity is sealed in such a way that the pumping medium cannot flow between the surfaces of the pressure plate and the pump housing, i.e. the passage is sealed from other pressure areas.
An embodiment is preferred in which the second connection of the intermediate capacity that opens into the pump chamber wall has a circular cross section. Openings such as this can be produced especially simply using drilling, punching or eroding, whereby material-removing methods are preferred in which no chips develop.
In one embodiment, it is provided that the opening area of the second connection is circular. However, in another embodiment it can be provided that this opening area in the pump chamber wall is expanded at least in some areas. This means that opening cross section expansions can be provided that can be formed e.g. by slots in the pump chamber wall. Because of the slots, influence can also be exerted on the volume flow that flows into the cell to be filled. In addition, the slots can have a constant or a changing cross section. This means that the volume flow entering the cell to be filled can be influenced in relationship to the rotational position of the pump element. In addition, a slowly increasing volume flow can be provided if slots are used whose cross section is smaller in the direction opposite the direction of rotation of the rotor. This is especially advantageous with low degrees of foaming.
Naturally the pump can have several suction and pressure connections. This means that a multi-stroke pump can be provided, whereby intermediate capacities are designed according to the number of pressure connections. Preferably one intermediate capacity is thus provided for each pressure connection.
In an especially preferred case, the pump according to the invention is a vane-cell or roller-cell pump in which the pump elements are formed as vanes or rollers. In an especially preferred case, the pump is used in automatic transmissions for the supply of operating medium for the engine speed transferring means and/or hydraulic control elements since especially in automatic transmissions oil is present with greatly differing degrees of foaming.
In one embodiment of the pump, one of the pressure plates is supported against the pump housing by way of a spacer as is described in DE 199 00 927 A1.
In addition, an embodiment is preferred in which the pressure connection and/or the suction connection has an opening expansion so that the pressure-compensating process is controlled both by the intermediate capacity and by the slots.